Yang Xia

Highly efficient electrolytic exfoliation of graphite into graphene sheets based on Li ions intercalation–expansion–microexplosion mechanism

In this communication, we report a facile and novel molten salt electrolysis method to prepare high-quality graphene sheets. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed that the final products exfoliated from the electrolysis of graphite cathode in the molten LiOH medium are mainly graphene sheets (approx. 80 wt% conversion efficiency). Raman spectroscopy revealed that the as-formed graphene sheets have significantly low density of defects. Based on these observations, the exfoliation mechanism of graphite cathode into graphene sheets through lithium intercalation–expansion–microexplosion processes was proposed. The discovery of a molten salt electrolysis method presents us with the possibility for large scale and continuous production of graphene.

Biotemplating of phosphate hierarchical rechargeable LiFePO4/C spirulina microstructures

Here, we report a new biotemplating method to synthesize hierarchical LiFePO4/C microstructures using native spirulina as both the carbon source and the template. Owing to its unique hierarchical microstructure, spirulina-templated LiFePO4/C exhibits remarkable electrochemical performance as cathode materials for lithium ion batteries. This facile strategy may open avenues towards replicating specific biological structures for phosphate materials in other potential applications.

A generic bamboo-based carbothermal method for preparing carbide (SiC, B4C, TiC, TaC, NbC, TixNb1−xC, and TaxNb1−xC) nanowires

Finding a general procedure to produce a whole class of materials in a similar way is a desired goal of materials chemistry. In this work, we report a new bamboo-based carbothermal method to prepare nanowires of covalent carbides (SiC and B4C) and interstitial carbides (TiC, TaC, NbC, TixNb1−xC, and TaxNb1−xC). The use of natural nanoporous bamboo as both the renewable carbon source and the template for the formation of catalyst particles greatly simplifies the synthesis process. Based on the structural, morphological and elemental analysis, volatile oxides or halides assisted vapour–liquid–solid growth mechanism was proposed. This bamboo based carbothermal method can be generalized to other carbide systems, providing a general, one-pot, convenient, low-cost, nontoxic, mass production, and innovative strategy for the synthesis of carbide nanostructures.

Tunable pseudocapacitance storage of MXene by cation pillaring for high performance sodium-ion capacitors

2D transition metal carbide materials called MXene have attracted significant interest in the field of electrochemical energy storage due to their high electrical conductivity and high volumetric capacity. However, the low capacity accompanied by sluggish sodiation kinetics of electrodes made from multi-layer MXene has limited their further application for sodium ion storage. The key challenge to overcome the abovementioned issue is to decrease the Na+ diffusion barrier and increase the active site concentration in MXene electrodes used for Na+ storage. In this study, a method to significantly improve the capacity and kinetics of Ti3C2 MXene for Na+ storage using facile alkali metal ion pillaring is reported. After Na+ pillaring, the MXene sheets (Na–Ti3C2) with incremental interlayer spacing exhibit a high reversible capacity of 175 mA h g−1 (∼170% of the original value) at 0.1 A g−1 and an excellent outstanding cycling stability for 2000 cycles at 2.0 A g−1 for sodium ion storage. By combining ex situ XPS with kinetics analysis, the increased number of active sites and lower Na+ diffusion barrier were confirmed after Na+ pillaring when compared with the cases of Ti3C2, Li–Ti3C2, and K–Ti3C2. The role of the terminal groups (–OH) in Na–Ti3C2 has also been confirmed by analysis of the electrochemical performance of the annealed Na–Ti3C2 samples (450 °C and 700 °C). The results show that the existence of –OH groups in Na–Ti3C2 can increase the number of Na+ storage active sites, but decrease the kinetics. By coupling the Na–Ti3C2 anode with an AC cathode, the assembled SIC device delivers a high energy density of 80.2 W h kg−1 and high power density (6172 W kg−1) with an ultra-long and stable cycling performance (capacity retention: ∼78.4 at 2 A g−1 after 15u2006000 cycles).

One-Step Synthesis of Asphalt Based Li3V2(PO4)3/C Nanocomposites as Cathode Materials for Lithium-Ion Batteries

A new kind of cathode materials, Li3V2(PO4)3/C nanocomposites, has been prepared via one-step solid-state reaction using ultra low-cost asphalt as both reduction agents and carbon sources. The asphalt is contained 60.37% of fixed carbon and 0.18% of other impurity.It is purchased from Zhen jiang Xin Guang Metallurgical Subsidiary Material Plant. Structural analysis shows that the obtained Li3V2(PO4)3/C nanocomposites contain abundant Li3V2(PO4)3 nanorods and micro/nano particles encapsulate with carbon shells. The Li3V2(PO4)3/C nanocomposites achieve enhanced dischargeability, reversibility, and cycleability. Electrochemical tests show that the Li3V2(PO4)3/C nanocomposite has initial discharge capacities of 170 mAhg-1 at 0.1C in the voltage range of 3.0 to 4.8 V. The improved electrochemical properties of the Li3V2(PO4)3/C nanocomposites are attributed to the presence of Li3V2(PO4)3/C nanorods and the electronically conductive carbon shell. This one-step solid state reaction using low-cost asphalt as carbon sources is feasible for the preparation of the Li3V2(PO4)3/C nanocomposites which can offer favorable properties for commercial applications.

Controlled Crystallization Synthesis of Porous FePO4·3H2O Micro-Spheres for Fabricating High Performance LiFePO4/C Cathode Materials

Amorphous porous FePO4·3H2O micro-spheres were synthesized via a controlled crystallization method. These micro-spheres have a particle size distribution from 10 to 28 μm. There are larger numbers of pores on the surface of FePO4·3H2O microspheres, which are important to synthesize high performance LiFePO4 cathode materials for the application of lithium ion battery. The electrochemical properties of the LiFePO4/C electrode, preparing by using the above porous spherical FePO4·3H2O particles, were measured. The electrochemical results show that the obtained LiFePO4/C has a high initial discharge specific capacity of 141.4 mAhg-1 and good cycling performance at 0.5 C. The microstructural and electrochemical analyses indicate that this porous spherical FePO4·3H2O is a fascinating precursor for preparing LiFePO4/C cathode materials.